Two-group disconnections are better than one

This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one. 

Nucleophile attack on the less hindered terminal carbon atom of the epoxide gives us the type of compound we want, and this was how the target molecule was made. 

Drug molecules often have 1,2-related functional groups 2-amino alcohols form one important class. Phenyramidol, for example, is a muscle relaxant. A simple two-group disconnection takes it straight back to 2-amino pyridine and styrene oxide. 

Notice that we have written 1,2-diX above the arrow to show that it s a two-group ( diX ) disconnection—we ve also numbered the carbon atoms in the starting material to show the 1,2-relationship, It may seem trivial in such a simple example, but it s a useful part of the process of writing retrosynthetic analyses because it helps you to spot opportunities for making two-group disconnections. 

The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more 

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Two-group disconnections are better than one-group disconnections... 

TWO-GROUP DISCONNECTIONS ARE BETTER THAN ONE-GROUP DISCONNECTIONS... 

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